The present invention relates to a method of manufacturing golf balls having a core, a cover and, optionally, one or more intermediate layer between the core and the cover. More particularly, the invention relates to a golf ball manufacturing method which can be advantageously employed to produce very stylish golf balls having highly transparent covers.
Golf ball development has hitherto been focused primarily on improving the basic performance of the ball, such as the distance, controllability, durability and feel on impact. From the standpoint of visibility and other considerations, the color of the ball has been predominantly white, which is an expansive color.
However, the base of golfers has expanded recently to include also young adults and women, leading to a rise in demand for golf balls which not only satisfy the basic performance requirements, but also have a distinctive appearance and convey a sense of the golfer's individuality. In response to such a demand, golf balls having an unusual appearance, such as golf balls which change in color when exposed to ultraviolet radiation (published U.S. Patent Application No. 2004/0266553) and golf balls which use phosphorescent pigments (published U.S. Patent Application No. 2004/0266554), have hitherto been described by golf ball suppliers.
The present applicant earlier disclosed, in JP-A 2007-136171, a golf ball which, in order to enhance the visibility and stylishness of the ball, has the quality of changing color (photochromism) depending on the type of light that strikes the ball.
In addition, golf balls with a cover made of transparent or translucent resin formed over either a core or a sphere composed of a core encased by one or more intermediate layer have been disclosed as highly stylish golf balls of distinctive appearance. Such balls often have a sense of transparency and leave the consumer with an impression of quality and elegance. By also mixing a pigment into the resin, unprecedentedly bright colors can be expressed.
However, in the foregoing golf balls having a highly transparent cover, the ball coloration is sometimes affected by the color of the layer in contact with the cover on the inside thereof (in the present invention, this layer refers to the core or the outermost intermediate layer, and is denoted below as the “layer adjacent to the cover”). For example, when a highly transparent material is used to form a cover over a core having dark gray color, the color of the core ends up being visible through the cover. In such a case, even when the cover has been colored to some degree, the core color cannot be completely hidden; as a result, the ball coloration ends up being tinged with gray. On the other hand, if a large amount of pigment, filler and the like is included in the above material so as to completely hide the color of the core, the resulting ball loses its transparent feel, making it difficult to achieve a bright color. In such cases, to reduce the influence by the color of the layer adjacent to the cover on the ball coloration, it is common to have this layer be white.
In order to respond to the diverse needs of the market, golf ball production at a manufacturing plant ordinarily involves the concurrent production of a plurality of types of golf balls having different performance characteristics such as distance and controllability. From a production control standpoint, the preformed body fabricated prior to formation of the cover is often transferred to a temporary storage place following fabrication and stored until such time as the cover is formed. The preformed body which matches the cover to be formed is then selected from among a plurality of types of preformed bodies stored at the temporary storage place, and supplied to the cover-forming step. In golf balls having a normal white color, the preformed bodies can easily be distinguished from one another by varying the color of the preformed body for each type of ball. In the present invention, “preformed body” refers to a core or a sphere composed of a core encased by one or more intermediate layer. Also, the outermost layer of such a preformed body corresponds to the “layer adjacent to the cover” as defined above.
In golf balls having a highly transparent cover, to keep the color of the preformed body from affecting coloration of the ball following cover formation, all the preformed bodies are fabricated so as to be white under visible light, regardless of the type thereof. As a result, the preformed bodies stored at a temporary storage place, in spite of minor differences by type in such properties as diameter and weight, are substantially identical in appearance. Hence, when selecting preformed bodies to be fed to the cover-forming step, it is difficult to distinguish between the different types based on their appearance. In the past, the preformed body matching a cover to be formed has been identified and selected from a plurality of types by checking the diameter and weight each time, but such identification is time-consuming, lowering productivity. Moreover, should the wrong type of preformed body be selected, the result is a defective product.
Accordingly, in the production of the above-described golf balls having a highly transparent cover, from the standpoint of improving productivity, there exists a desire for a way to easily and reliably identify, from among preformed bodies of different types but the same color, a preformed body which matches the cover to be formed.